Various devices such as personal computers, digital cameras, and video cameras are designed so as to store contents. To minimize the trouble of managing those contents, a home server is employed that acquires the contents from the mentioned devices and performs is centralized management of the contents. The device from which the home server acquires the contents will hereinafter be referred to as client device.
The client device transfers the contents to the home server through a network connected via an Ethernet (registered trademark) cable, a wireless local area network (LAN), or the like. The contents can also be transferred from the client device to the home server through a communication cable such as a universal serial bus (USB) cable or a card medium such as a memory card, instead of the network.
It is generally senseless to acquire again a content once acquired from the client device, and hence the home server does not duplicately acquire the same content. Acquiring the same content from the client device each time not only prolongs the time for the acquisition procedure, but also leads to over-consumption of the storage capacity of the home server. In the case where it is necessary to make a duplication of an already acquired content, it is generally less time-consuming and less troublesome to copy that content in the home server, than acquiring the content again from the client device.
Conventional methods of deciding whether a content stored in the client device (hereinafter, candidate content) has already been acquired by the home server, in order to avoid duplicate acquisition of the content already acquired from the client device, include employing a content identifier such as a file name or a content ID. In this case, the home server first acquires, from the client device, an identifier list of the contents stored in the client device. Then the home server compares the acquired identifier list with all the content identifiers previously acquired by the home server, to thereby identify an unacquired content and acquire only the unacquired content from the client device.
Another example of the conventional methods of deciding whether the candidate content has already been acquired by the home server is employing property information assigned to the contents (for example, see PTL 1). In this case, the home server compares the property information assigned to the already acquired contents with the property information assigned to the contents stored in the client device, to thereby identify an unacquired content and acquire the same.
Still another example of the conventional methods of deciding whether the candidate content has already been acquired by the home server is transmitting information about an untransferred content from the client device to the home server (for example, see PTL 2). In this case, the client device associates each of the stored contents with information that indicates whether the content has been transferred to the home server, and transmits the information about the untransferred content to the home server in response to a request from the home server or at a predetermined timing. The home server identifies the unacquired content on the basis of the information transmitted by the client device, and acquires the same.
In addition, the conventional methods of deciding whether the candidate content has already been acquired by the home server Include comparing the substance of the content (for example, see PTL 3 and PTL 4). In this case, the home server compares the concrete substance between the already acquired contents and the candidate content in the client device, to thereby decide whether the candidate content in the client device has already been acquired, and acquires the candidate content in the case where it has not been acquired, and stores the same in the storage unit.